*{
    margin: 0;
    padding: 0;
}

html, body{
    height: 100%;
}

#left{
    width: 200px;
    height: 100%;
    background-color: rgb(255, 0, 0);
    float: left;
}

#center{
    width: calc(100% - 400px);/* 减号前后必须空格 */
    height: 100%;
    background-color: rgb(0, 255, 0);
    float: left;
}

#right{
    width: 200px;
    height: 100%;
    background-color: blue;
    float: right;
}